Conversions and Chemical Equations

Question

When propane (C3H8) reacts with oxygen (O2), carbon dioxide (CO2) and water (H2O) are produced. The balanced equation for this reaction is:

C_3 H_8 (g)+5 O_2 (g)→3 〖CO〗_2+4 H_2 O(g)

If 20 moles of oxygen react,

The reaction consumes ___________ moles of propane (C3H8).

The reaction produces___________ moles of carbon dioxide and

___________ moles of water.

Answer 1

For each scenario, we will use the mole-mole ratio to jump from moles of one molecule to moles of another. These are the coefficients in front of each molecule in the balanced equation.

mole ratio = what you want / what you have

New moles = old moles * mole ratio

a)

What we start with is 20 mol of O2 = old moles

We want to go into mol C3H8 = new moles

We will use their coefficients to make a mol ratio

Coefficient of C3H8 = 1 (there is no number there)

1 = what we want

Coefficient of O2 = 5

5 = what we have

mole ratio = 1/5

New moles C3H8 = old molesO2 20 * 1/5 ratio = 4

If 20 mol O2 react, 4 mol C3H8 are consumed

b) for CO2, the coefficient is 3

for H2O, the coefficient is 4

for O2, the coefficient is 5

CO2 ratio: 3/5

H2O ratio: 4/5

CO2 new moles = 20 * 3/5 = 12 moles CO2 produced

H2O new moles = 20 * 4/5 = 16 moles H2O produced